You're completely right. I have all three books now (and each is useful in a different way), but I find the podcasts give me good mini-nudges when my motivation lags. And often hearing something phrased in a unique way will give me a new understanding of one of the concepts.

This podcast you linked was especially refreshing, in hearing that even the pros aren't getting to inbox zero daily. I do still need improvement on the collect/process/review cycle, but it's nice to have a reminder that it's still going to be flexible around what life throws at you. :)